Cross-Origin-Resource-Policy middleware

This middleware sets the Cross-Origin-Resource-Policy header. Read about it in the spec.

Usage:

``javascript
const crossOriginResourcePolicy = require("cross-origin-resource-policy");

// Sets "Cross-Origin-Resource-Policy: same-origin"
app.use(crossOriginResourcePolicy({ policy: "same-origin" }));

// Sets "Cross-Origin-Resource-Policy: same-site"
app.use(crossOriginResourcePolicy({ policy: "same-site" }));
``